A method and device for estimating the opacity at a point of a scene lit by an area light source and comprising an object defined by a mesh and occluding some of the emitted light. In order to optimize the calculations for live estimation of the opacity, the method comprises sampling said area light source in a plurality of samples, for at least one sample of the plurality of samples and for at least one first mesh element of the occluding object visible from the at least one sample, generating one shadow plane per edge of the at least one first mesh element, estimating a opacity level depending on coefficients of projection in a function base from values representative of the opacity for a set of intersection points between at least one ray having for origin a viewpoint of the scene and shadow planes crossed by said at least one ray, depending on an angle formed by the normal associated with each shadow plane crossed and by said at least one ray.